Mostly in TD-SCDMA networks, a UE is moved in an N-frequency scenario during connected mode, i.e., during Mobile Originating (MO) or Mobile Terminating (MT) circuit switch call and packet switch call. The serving cell measurements are done on the primary frequency, while the secondary frequencies are used for Down Link (DL) and Up Link (UL) data transfer. Additionally, a UE is assigned one secondary frequency for the data transfer. The N-frequency concept is used in TD-SCDMA networks to ensure less interference in the primary frequency. However, very high interference may be observed by the UEs in the secondary frequencies caused by the reuse of these secondary frequencies amongst the neighboring cells. This may result in drop of Downlink Physical Channel Signal to Noise Ratio (DPCH SNR), which further results in drop of Signal to Interference Ratio (SIR) beyond an acceptable threshold.
In conventional systems, this SIR drop may be overcome by selecting new serving cells. However, in TD-SCDMA networks, interference is not observed in the primary frequency, but in data slots of the secondary frequencies. Moreover, as new serving cell selection is made based on the primary frequency, the UE may end up selecting the current serving cell repeatedly. As a result, the UE is not able to select a new cell in order to resolve the issue of interference in the data slots. This further results in frequent call drops, thereby, impacting user experience.